package com.batchengine.db.handlers;

import com.batchengine.db.ResultSetHandler;

import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * <code>ResultSetHandler</code> implementation that converts one
 * <code>ResultSet</code> column into an Object. This class is thread safe.
 *
 * @see com.batchengine.db.ResultSetHandler
 */
public class ScalarHandler implements ResultSetHandler {

    /**
     * The column number to retrieve.
     */
    private int columnIndex = 1;

    /**
     * The column name to retrieve.  Either columnName or columnIndex
     * will be used but never both.
     */
    private String columnName = null;

    /**
     * Creates a new instance of ScalarHandler.  The first column will
     * be returned from <code>handle()</code>.
     */
    public ScalarHandler() {
        super();
    }

    /**
     * Creates a new instance of ScalarHandler.
     *
     * @param columnIndex The index of the column to retrieve from the
     *                    <code>ResultSet</code>.
     */
    public ScalarHandler(int columnIndex) {
        this.columnIndex = columnIndex;
    }

    /**
     * Creates a new instance of ScalarHandler.
     *
     * @param columnName The name of the column to retrieve from the
     *                   <code>ResultSet</code>.
     */
    public ScalarHandler(String columnName) {
        this.columnName = columnName;
    }

    /**
     * Returns one <code>ResultSet</code> column as an object via the
     * <code>ResultSet.getObject()</code> method that performs type
     * conversions.
     *
     * @return The column or <code>null</code> if there are no rows in
     *         the <code>ResultSet</code>.
     * @throws SQLException if a database access error occurs
     * @see com.batchengine.db.ResultSetHandler#handle(java.sql.ResultSet)
     */
    public Object handle(ResultSet rs) throws SQLException {

        if (rs.next()) {
            if (this.columnName == null) {
                return rs.getObject(this.columnIndex);
            } else {
                return rs.getObject(this.columnName);
            }

        } else {
            return null;
        }
    }
}
